Stator for a.c. motor



Oct- 2, 1962 J. LUDEMANN ET AL 3,056896 STATOR FOR A.C. MOTOR Filed Nov. 5, 1959 Jnvenfo 115 JOSEPH LUDEMAN/V HEINZ HEILMANN yf/M2ninb Af/z9f/7g 5 United States Patet 3,056,896 STATOR FOR A.C. MGTOR Joseph Ludemann and Heinz Hei1mann, Oldenburg, Germany, assignors 10 Licentia Patent-Verwaltungs- G.m.b.1L, Frankfurt am Main, Germany Fileal Nov. 3, 1959, Sex. N0. 850,620 Clams priority, application Germany Nov. 10, 1958 6 Claims. (Cl. 310-258) The present invention relates to alternating current motors. More in particular, the present lnvention relates to stators in singler polyphase alternating current motors having a plurality of salient poles arranged in pairs, and wherein the number of such pairs is greater than 1.

It ls known to provide different types of stators for small singleor polyphase asynchronous motors having not more than one pair of salient poles. The most commonly employed type cf stator comprises leakage bridge portions between the respective edges of the poles.

lt has also become known to use stators With an improved structure in asynchronous motors wlth not more than one pair cf salient poles, according to which a 121minated star-shaped po-le structure bearing the magnetic coils is pressed into a stator yoke. According to still another improved structure a laminated pole ring 1's disposed in the pole bore. The application of these improved structures to A.C.-motors With -more than one pair of salient poles has met, however, with considerable prejudice. As a matter of fact, the high magnetic stray effect has proved to be prohibitive of the application 0f the afore-mentioned structures, as the electrical properties of the motors provided with such stators were highly unsatisfactory.

With the foregoing in mind lt is the object of the present invention t0 provide a structurally improved stator for singleor polyphase alternating current motors with a plurality of salient poles arranged in pairs, comprising more than one pair of salient poles, wherein the magnetic stray flux is greatly reduced.

This object is achieved by the present invention Wherein the air gap between the stator and the rotor is enlarged in the area cf the auxiliary poles. This can be done by providing the inwardly directed portions of the auxiliary poles With a recess.

Prefe1ably, the recess extends 011 either side of the auxiliary poles into part of the adjo-inlng bridge portions. The thickness 01 the bridge portions 1's kept as small as possible and preferably does not exceed approximately 0.8 millimeter.

This invention will be further described With reference to the accompanying drawings, wherein FIGURE 1 is a sectional view of a conventional bipolar stator w1'th a star-shaped salient pole arrangement;

FIGURE 2 is a sectional view of a four-pole stator of the present invention witl1 a star-shaped pole arrangernent;

FIGURE 3 is a sectional view of a four-.pole stator of the present invention With a pole-ring.

Referring now to the drawings more in detail and turning first to FIGURE 1, the conventional stator comprises a yoke ring 6 and an inner spider -1 i.e. a star-shaped pole structure forming a separate unit not connected with yoke 6. The inner spider 1 is tlghtly fitted into the yoke ring 6 and has two main poles 2 disposed opposite to each other, two auxiliary poles 3 also disposed opposite to each other, and four leakage bridge portions connecting the varlous poles With one another. The inwardly extending pole and bridge portions define a circle and thus enclose a cylindrical roter space 5.

Turning now t0 FIGURE 2, the stator of the present lnvention is adapted for use With motors having more than one pair cf salient poles. As shown in FIGURE 2,

2 the stator of the invention comprises, as a yoke, a yoke ring 12, and an inner spider, i.e. a star-shaped pole structure formlng a separate unit. lt is tightly fitted into the yoke ring 12.

The inner spider 7 has four main poles 8 and four auxiliary poles 9, the main and auxiliary poles being a1- ranged in oppositely disposed pairs. The poles are counected Wlth one another by the leakage bridge portions 19.

According to the present invention, the air gap between the roter and the stator is enlarged in the area of the auxiliary poles. As shown in FIGURE 2, the pole surfaces 0 f the auxiliary poles 9 directed towards the rotor space 211 have recesses 11. Due to these recesses 11 the air gap between the stator and the roter in the rotor space 26 is enlarged. The roter space is thus defined difierently from the conventional rotor space shown in FIGURE 1. Whereas in FIGURE 1 the inwardly directed pole and bridge portlons describe, in section, a full circle, the bridge and recessed pole portions of the stator 0f the invention shown in FIGURE 2 deseribe, in section, segments of a circle with a plurality of outward- 1y bulged portions, defining the rotor space 20.

It has been found to be of particular advantage to extend the recessed portions 11 on either side into part of the adjoining bridge portions, as shown in FIGURE 2. The recesses 11 thus extend across the auxiliary poles 9 and, on either side 0f each auxiliary pole, over a part 0f each cf the adjoining leakage bridge portions 19, as shown by the recess portions 11a, 11b of recess 11.

It is also advantageous to provide laminated bridge portions 19 which have a minimum thickness, preferably not exceeding approximately 0.8 millimeter.

The au'joining surfaces 21, 22 of the poles and the yoke, respectively, can have any desired configuration allowing for the tightly fitting insertion of the inner spider into the yoke.

The basic feature of the invention can be also applied With equal advantages to stators wherein the poles are fixedly connected With the stator yoke. This is shown, for example, in FIGURE 3. The stator has four main poles 13 and four auxiliary poles 14 arranged in oppositely disposed pairs, and provided with rnain pole Wind- 1'ngs 17 and auxiliary pole windings 18, respectively. The poles 13 and 14 are fixedly connected with yoke 15 whereas the leakage bridge portions for-m a laminated pole ring 16, which is a separate structure, but tightly fitted into the yoke and pole portion of the stator. The adjoining surfaces 23, 24 o-f the poles and the pole ring, respectively can have any desired configuration allowlng for the tightly fitting insertion of the pole ring.

According to the invention, the laminated pole ring 16 constituting the leakage bridges between the poles is provided with recesses 25, corresponding to recesses 11 in FIGURE 2, and also preferably extending on either side into part of the adjoining bridge portions 19, as shown by the extended recess portions 25a, 25b.

Again, the thickness brldge portions forming the laminated pole ring 16 are kept as small as possible. and preferably d0 not exceed 0.8 millimeter.

The invention 0Ifers numerous advantages constituting a great progress over the art.

The recesses in the area of the auxiliary poles enlarge the air gap between the stator and rotor which greatly reduces the hanrnonic waves of the field curve of the auxiliary phase. At the same time, the leakage and main reactances o-f the auxiliary phase circuit are advantageously modified in the following manner:

The inductive leakage reactance of the auxiliary phase circuit is kept small in case of short-circuit, whereas it is increased in case of no-load operation, in connection with the decrease of the main reactance of the auxiliary phase. Consequently, the mutual capacitance of the auxiliary phase is connected in series with a great leakage inductance in case of no-load operation, whereas it is connected in series with a small leakage inductance in case of short-circuit. The total capacitance in the auxiliary phase circuit is thus variable i.e it is comparatively great during the short, but comparatively small under no-load operation. The motor has thus greatly improved starting as well as no-load operation characteristics.

The invention makes it possible to dispense with additional, cumbersome and costly means adapted by the art for adjusting the auxiliary phase circuit, depending on l-oad and number of revolutions. It is, -for exarnple, no longer necessary to equip the motor with starting capacitors, centrifugal circuit breakers er relays, controlled transdu-cer connections, saturated ironcore ehokes, and the 1ike.

The small thickness of the leakage bridge portions great- 1y reduces the 1eakage flux. Since the leakage bridge portions are also laminated, losses due to eddy currents are virtually negligible.

It will be understood that this invention is susceptible to modification in order to adapt it to difi"erent usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall Within the scope of the appended claims.

What we claim is:

1. In an alternating current motor having a rotor, a stator comprising a plurality of main salient poles disposed in pairs, said stator having at least one pair o=f such main salient poles, and a plurality of auxiliary salient poles, said rotor and said stator defining an air gap between each other which is enlarged in radial direction in the area of said auxiliary poles only.

2. In an ahernating current motor having a rotor a stator comprising a plurality of main salient poles disposed in pairs, said stator having at least one pair of such main salient poles, and a plurality of auxiliary salient poles said rotor and said stator defining an air gap between each other, said auxiliary salient poles having a re-- cess at the respective ends directed towards said rotor enlarging the air gap between said roter and said stator as compared with the corresponding air gap at said main stator comprising a plurality 0f main salient poles disposed in pairs, said stator having at least one pair 0f such main salient poles, and a plurality 0 f auxiliary salient poles, said rotor and said stator defining an air gap between each other, a plurality of leakage bridge portions between said main and said auxiliary salient poles, a plurality of recesses being provided in said auxiliary salient poles at the respective ends directed towards said roter, With the recesses extending at either side of said auxiliary salient poles into said leakage bridge portions, which recesses enlarge the air gap between said stator and said roter as compared with the air gap between said roter and said main poles.

4. A stator in an alternating current motor as described in claim 3, further comprising a yoke, said main and said auxiliary salient poles and said leakage bridge portions forming an integral star-shaped structure tightly fitting into said yoke.

5. In an alternating eurrent motor having a roter, a stator comprising a plurality -of rnain pole teeth disposed in pairs, said stator having one pair o-f such main pole teeth, and a plurality of auxiliary pole teeth, a yoke portion forming With said main and auxiliary pole teeth one integral structure, and a plurality of leakage bridge portions forming one integral larninated pole ring. tightly fitting against the respective ends of said main and said auxiliary pole teeth directed towards said said rotor, said leakage bridge portions forming said pole ring and said roter defining an air gap between each other, With a plurality of recesses being provided in said lea=kage bridge portions at the end facing said roter and the areas below said auxiliary poles, which recesses thus enlarge said air gap only below said auxiliary poles.

6. A stator in an alternating current motor as described in claim 3, said leakage bridge portions being formed as a lamination having a thickness not exceeding 0.8 millimeter.

References Cited in the file of this patent UNITED STATES PATENTS 1363167 Peugeot Dec. 21, 1920 1382,257 Turbayne Inne 21, 19'211 FOREIGN PATENTS 1040122 Germany Oct. 2, 1958 

